Field of the Invention
The present invention relates to a disconnection detection device, and in particular, to a disconnection detection device which detects disconnection (cut) of a wire harness connected to a low-resistance load circuits, such as an actuator or a horn.
Description of Related Art
An antitheft device for a vehicle has a detection sensor which detects abnormality relating to a theft of a vehicle, a sound generation device (siren) which generates alarm sound in order to make surrounding people recognize offenses and to issue a warning (including a threat) to a thief, and a main unit which determines presence or absence of a theft based on a detection signal from the detection sensor and controls the output of alarm sound. In regard to the antitheft device configured as above, in many vehicles, a horn device which is mounted as a standard feature in the vehicle and outputs horn sound or a separated horn (so-called security horn) is used as a siren (sound generation device).
A horn provided in the horn device is attached in an engine room or a vehicle front portion, such as a bumper attachment portion. For this reason, the thief inserts a tool or the like from a gap of a hood or a front grill, or a gap formed by prying or the like, whereby there is a problem in that the horn is destroyed. As a method of solving such a problem, a sound generation device for theft alarm and an antitheft control system described in Patent Literature 1: JP-A-2009-280001 are known. In the technique described in Patent Literature 1, a shield portion which resonates by the frequency of alarm sound generated from the horn is provided between the outside of the vehicle and the horn (siren for theft alarm), and the shield portion protects the horn. In addition, since the shield portion resonates at the frequency of alarm sound by alarm sound from the horn, the sound volume is prevented from being reduced due to alarm sound being shielded by the shield portion.
[Patent Literature 1] JP-A-2009-280001
However, in the invention described in Patent Literature 1, since it is necessary to provide the shield portion which is not directly related to the original function of the horn, there is a problem in that the weight or cost of the horn is increased. In addition, in order to prevent alarm sound (horn sound and howling sound) from the horn from being completely shielded, it is necessary to provide a gap between the horn and the shield portion, and there is a problem in that the attachment space of the horn is increased.
A general horn device has a horn which outputs horn sound, a horn button which is disposed in a steering wheel, a relay which has a contact circuit being opened or closed in conjunction with the on/off state of the horn button and controls the on/off state of supply of drive power to the horn, and a wire harness which electrically connects the relay and the horn.
In particular, the horn (including the security horn) is attached in the engine room or the vehicle front portion, such as the bumper attachment portion. For this reason, the thief inserts a tool or the like from the gap of the hood or the front grill, or the gap formed by prying or the like, whereby there is a problem in that the wire harness which supplies drive power to the horn is cut. Since drive power is not supplied to the horn due to the cut of the wire harness, there is a problem in that the effect of the antitheft device is substantially invalidated. Even in the configuration described in Patent Literature 1, since a main unit and the security horn are connected to each other by the wire harness, there is a concern that the same problem as in a case where a horn device is used as a sound generation device of an antitheft device occurs.
In a general vehicle, door locking and unlocking can be performed by a remote operation of an electronic key or a door lock switch in the vehicle as well as locking and unlocking a door using a key (engine key). In a vehicle in which door locking and unlocking can be performed by such a remote operation, a door lock motor (actuator for door lock) is mounted in each door, and drive power (drive signal) is supplied to each door lock motor from a controller through a wire harness. However, in the door lock mechanism configured as above, there is a concern that a thief cuts the wire harness in a transition portion of the door and supplies drive power from the cut wire harness on the door side to the door lock motor to actuate the door lock motor, thereby unlocking the door.